timediff: return timediff_t from the time diff functions

... to cater for systems with unsigned time_t variables.

- Renamed the functions to curlx_timediff and Curl_timediff_us.

- Added overflow protection for both of them in either direction for
  both 32 bit and 64 bit time_ts

- Reprefixed the curlx_time functions to use Curl_*

Reported-by: Peter Piekarski
Fixes #2004
Closes #2005

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/asyn-thread.c b/lib/asyn-thread.c
index a86772965..96babb728 100644
--- a/lib/asyn-thread.c
+++ b/lib/asyn-thread.c
@@ -535,7 +535,8 @@ CURLcode Curl_resolver_is_resolved(struct connectdata *conn,
   }
   else {
     /* poll for name lookup done with exponential backoff up to 250ms */
-    time_t elapsed = Curl_tvdiff(Curl_tvnow(), data->progress.t_startsingle);
+    timediff_t elapsed = Curl_timediff(Curl_tvnow(),
+                                       data->progress.t_startsingle);
     if(elapsed < 0)
       elapsed = 0;